Magic Jack.....How many GB does a phone call use?

Posted Sat August 8, 2009 12:00 pm, by James M. written to magicJack.com

I have purchased a magicJack and installed it on my computer. It works as long as I am connected to a high speed internet connection. I think that when that high speed internet connection is via my Verizon EVDO that I will exceed Verizon's 5GB limit in one 10 minute phone call.

After spending an hour with magicJack's customer service, the only information about data usage on my internet connection they would tell me was "80 to 120 kbs".

Please tell me if I will be able to use the magicJack without exceeding Verizon's limit. Since I am still within the magicJack 30 day trial, I can still return the unit if it will not work with my system.

I think they meant kilobits per second, kbps. They gave you enoughinformation to estimate the answer.

If they sample your voice at 8khz, (the bandwidth is 4khz and perNyquist you sample at twice the rate), and use 16 bits per sample,that would be 8000x16 = 128000 or 128kilobits per second. Wow, whatan expensive college education from decades ago can do for you. Ithink a lot of voice is lost over 3500Hz, so that may explain why therange goes lower. Of course this does not account for parity bits orerror correction, but 80-120kbps is in the ballpark.

Now all you have to do is convert for a 10 minute call (note kilo isused base 10 for data rates, but data storage uses base 2, so kilo is1024):

10*60 = 600 seconds. So, you multiply 120kbps by seconds to getkilobits (remember learning units in chemistry or physics?) 600*120 =72000 kilobits. There are 8 bits in a byte, so divide by 8 to get9000 kilobytes. There are 1024 kilobytes in a megabyte, so divide by1024. 9000/1024 = 8.79MB, which is greater than 5MB.

It looks like Magic Jack uses too much bandwidth.

I am frankly extremely surprised by this result. Voice-only exceedsthe data limit of a high speed internet connection over a 10 minuteperiod? Maybe my seat of the pants calculation is off, but it givesyou a starting point.

I never liked their commercials anyway. Now I'll be saying "you needMagic Jack" to myself all day...

Off the top of my head, I can't say for sure. However, if you'reusing EVDO with Verizon Wireless, I'd strongly recommend against usingsomething like MagicJack (or any VOIP). Besides Verizon looking downon this sort of thing (they could cancel you for doing it), there arereasonably steep data requirements.

Also, EVDO does not have the consistent throughput needed for qualityVOIP.

However, since you have 30 days, give it a try and see if you're happywith the quality. There are ways to measure your data usage, but theycan vary widely from what Verizon says. You might to call them andask if they can provide you accurate stats, perhaps for a 1 or 2 dayperiod.

By the way 120kbs would be about 15 kbytes/sec. Which would mean thatan hour call would be about 50MB. If that's the case, and you weren'totherwise using data (which I'm assuming is not the case), you'relooking at about 20 hours a month. That might be fine for your needs. (My math might be very off here, so someone else might need tocorrect me).

For reference, an average song download (3-5 minutes) is about 5-10MB.